P0170, p0173

[110reef]

I've been battling these two codes now for over a year, continuing to throw parts at them with no success. I even took it to a mechanic, but still have the codes. Any suggestions?

So far I have replaced the oil separator, various vacuum hoses, the O2 sensors, several other parts as well. The car runs great, but I cannot pass inspection the way it is.

I am trying to remember whether I replaced the MAF or not, or cleaned it or what. I think I have but I may be mixing it up with another of my cars. I was thinking of doing that next.

Any help as to what to look at next?

[Eric93se]

So they are fuel trim codes. Did your mechanic smoke test the vacuum system? Has the valve cover ever been replaced? because that can also leak vacuum. Another possibility is the SAP (secondary air pump) it is possible that the valve that connects to the exhaust manifold can leak. You say oxygen sensors have been done, there are 4 all together and the pre-cat sensors are the important ones. Another possibility is leaking injectors, I would run a bottle of injector cleaner with the next 3 tanks of gas, use a different brand each time.

[XnWarden]

Running lean on both banks? I'd suspect the maf sensor or a bad vacuum leak

Sent from my VS987 using Tapatalk

[ed323i]

To get a trim error that's caused by a vacuum leak, it should be a quite big vacuum leak that you should be able to hear with the engine idling.. Smoke test is the easiest to find it. Or connect a vacuum cleaner to the intake manifold rubber boot, and improvise some sort of seal with tape/plastic bags. Then you should be able to find it.

If it's not a vacuum leak, and the O2 sensors have indeed been replaced, I would test fuel pressure. If the fuel pressure regulator (or a very worn out fuel pump) isn't supplying the right pressure, a fuel trim error will be the result.

Running an INPA live sensor values diagnosis will also help a lot. Check all live sensor values and then check the lambda trim values. Then you'll know if the DME is adding or removing injector time and that can help diagnose the problem. If there is a vacuum leak then the DME has to add fuel. If the fuel pressure regulator is supplying too high pressure, it will lower fuel. If the FPR/fuel pump is supplying too low pressure, it will add fuel.

You can also see what the O2 sensors are saying and if they are oscillating between high and low voltage frequently. And you'll immediately see if both pre-cat O2 sensors give comparable values (which they should if all injectors are okay). And check all temperature sensors.

All you need is a Windows laptop, install all the INPA software, and buy an USB-OBD2 cable.. The investment will pay itself back in no-time, because it takes away the guessing (and unnecessary part replacing) and gives the real reasons in many cases (not always though).

P.S. Also, you can reset the codes, then disconnect the MAF sensor, and drive a little while.. Then see if the codes remain gone.. If so, then reconnect the MAF and take another drive. If the errors return, you need another MAF.. Only buy Siemens / VDO.. Never buy a cheap Chinese clone MAF.. I've tried 3 of these (it became an experiment) and none of them worked well.

Good luck!